Motor-control system.



t R. H. MQLAIN.

MOTOR CONTROL SYSTEM} APPLICATION FILED NOV. 25, 1912.

Patented Sept. 2, 1913.

lm/entor Robert H. M- Lain His o tfioorneg Witnesses STATES PATENT OFFICE...

ROBERT H. MCIJAIN, OF SCHENECTADY, NEW YORK; ASSIGNOE'TO"GENEBALELECTRIC COMPANY, A CORPORATION OF NEW 'YORKE- I MOTOR-CONTROL SYSTEM.

To all whom it may concern Be it known that I, ROBERT H. MoLAIN, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, haveinventedcertain new and useful Improvements in Motor-ControlSys terms, of which the following is a speclfication.

This invention relates to the control ofelectric motors and has for its object the provision of means whereby an electric motor may be started, stopped and generally controlledin a safe, eflicient andsimple manner.

My invention relates more specificallyto the control of'electricmotors operating on whatis known as-the Ward Leonard system inwhichthe speed of the motor is controlled by varyin the voltage of the the \fact that the motor cannot accelerate rapidly enough to 'generate a counter-electromotive force sufiicient to keep the current within safe limits. Likewise during the retardation, if the voltage of thegenerator is reduced'too rapidly an overload will also occur by reason of the fact that the motor acting as a generator will cause the current to rise above a safe value.

- One of the objects of my invention is to provide means for-protectingthe apparatus rom such overloads. In carrying out this object I employ in addition to the shunt field of the generator a-series field which is preferably wound differential-1y. with respect to the shunt field. This series field is short circuited during normaloperation but'the short circuit is opened whenever the current rises above a predetermined value. During the accelerationof the motor, therefore, upon a predetermined 'rise in current, the series field will be inserted to oppose or buck the-shunt field and thereby reduce the voltage of the generator and ence the current. The arrangement"is such that during acceleration ofdthe overload relay will operate.

continuously to open and close the short cir- Specifieation of Letters Patents Application filed November 25, 1912. Serial No. 733,275.

' invention shunt cuit on the series field in response to variations in the current due to the efi'ect of the Patented Sept. 2,1913

this latter case the current'through the sedirection and the two fields will therefore assist each other to boost the voltage. When, therefore, the current rises above a predetermined Value during retardation the voltage will be-boosted to oppose the voltage impressed by the motor acting as a generator. In either case the overload relay w'ill operate continuously and rapidly to open and ries field will be reversed While the current through the shunt field will be in-the sameclose-the short circuit on the series field until the motor reaches a fi'xed speed.

Other objects and purposes. of my invention will appear in the course of the following specification in which I'have shown my invention embodied in concrete form for purposes of illustration.

,Referring .to the drawing which shows my diagrammatically in a specific form, Arepresents the armature of the motor Mto be controlled'andF' the field of .the motor-which in this caseis separately excited from the mains a a. A represents the armature of the generator 6' for supplying the motor and F represents the shunt field of the generator whichis also separately excited from the mains a a. The strength of this shunt fi'eld is varied by 'means of the resistance R 'controlled by the controller G in a well understood manner. As thus far described the apparatus constitutes the well known Ward Leonard system of motor control.-

'S represents a series field "fort-he genera tor G which is preferably wound differentially with respect to the shunt field F so that when the series field is in circuit .it will oppose or buck the magnetism of the field so as to reduce the voltage of'the generator. This series field 'is "controlled by an overload relayO connected in the power circuit between the motorand generator. When the current rises above a predetermined value the coreofthe overload relay will lift and o n'the short circuit upon the series field. ince the currentto be controlled in opening and closlng the shbrt'clrcuit-of the series field may be, and generally is, quite large, I may employ an electromagnetic switch B which is designed for "controlling large currents for opening and closing the circuit. This switch will have its energizing winding connected across the line a a and will be controlled by the overload relay B. The switch B will be closed during normal operation and will be only opened when the current in the overload relay rises above a predetermined value.

The operation of my device is as follows: To start the motor the line switch D is first closed which energizes the field F of the motor and also energizes the winding of the switch B to short circuit the series field S. The controller is now turned in one direction or the other depending upon the r0- tation of the motor desired to energize the field F of the generator through the resistance R. If the resistance is cut out of the field of the generator too rapidly, the current in the motor circuitwill rise above a predetermined value so as to operate the overload relay 0 which will cause the switch B to open and insert the series field S. The series field being wound differentially with respect to the shunt field winding F the voltage of the generator will be reduced and the current correspondingly reduced. The reduction of the current causes the overload relay to close whichin turn causes switch B to close to again short circuit the series field. This opening and closing of the short circuit on the series field will continue rapidly until the current reachesnormal value. If desired the operator can move the controller to the full on position so as to entirely short circuit the resistance but the overload relay will protect the apparatus by vibrating rapidly and opening and closing the short circuit on the series field until the motor reaches a sufii-' cient speed to bring the motor current down to normal. If now the operator throws the controller handle toward the oil position so as to decrease the voltage on the generator too. rapidly the motor acting as a generator will causean excess current as is wellunderstood. As soon as the current rises above a predetermined value the over-' load relay will operate and open the short circuit on the series fieldj The current in the series field now, however, is reversed and the magnetism of the series field will therefore assist the shunt field and boost the voltage to oppose the voltage of the motor acting as a generator. This will reduce the current as before and the overload relay will close. The short circuit on the series field will likewise in this case be opened and closed rapidly until the current reaches a normal value.

in the opposite direction so as to reverse To reverse the direction of rotation of the motor the controller is turned the current in the field of the generator and the operation will be the same as above described.

With this arrangement it will be seen that a single overload relay controls the circuit for both accelerating and retarding and it would be impossible for the operator to from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire tosecure by Letters Patent of the United States, is,

1. The combination with a separately excited motor, and a generator for supplying current to the armature of said motor, means for varying the voltage of the generator to vary the speed of the motor, a series field for said generator, and an overload relay' for controlling said series field.

2. The combination with a separately excited motor and a generator having a shunt field for supplying current to the armature of said motor, means for varying the strength of said shunt field to varythe speed of the motor, a series field for said generator, and an overload relay for controlling said series field.

3. The combination with a separately excited motor and a generator having a shunt field for supplying current to the armature of said motor, means for varying the generator wound difi'erentially with respect to the shunt field, and an overload relay for controlling said series field. V

4. The combination with a separately-excited motor and a generator having a shunt field winding for supplying current to the armature of said motor, means for varying the strength of said shunt field to vary the speed of the motor, a series field for the generator short circuited during normal operation and difierentially wound with respect to the shunt field winding, and an overload relay for opening said short circuit to insert the series winding when the motor current rises above a predetermined value.

5. The combination with a separately excited motor and a generator having a'shunt field winding for supplying current to the armature of said motor, means for accelerat- 111g the strength of said shunt field, a series field for the generator short circuited dur-' ing normal operation and differentially wound with respect to the shunt field windand retarding said motor by varying ing, and an overload relay responsive to In witness whereof, I have hereunto'set variations in current due to the effect of said my hand this 22nd day of November, 1912. series field upon the voltage for continu ROBERT H. MOLAIN. ously opening and closing said short circuit Witnesses:

-' during the accelerating. and retarding of the HELEN ORFORD,

motor. BENJAMIN B. HULL. 

